Method for obtaining spheroidal graphite castings

ABSTRACT

A method for obtaining castings of spheroidal graphite iron, by treatment of the iron with a nodularizing agent, comprising filling a pouring ladle with liquid iron pouring the iron from the ladle into a mould in the form of a stream of iron and incorporating the nodularizing agent into the stream of iron in a region between the pouring ladle and the mould and as near as possible to the mould. A device for carrying out said method comprises a pouring ladle and a mould, a pouring channel between the ladle and the mould and a device for supplying nodularizing agent combined with the pouring channel.

United States Patent [191 DeGois et a1.

[ Nov. 4, 1975 METHOD FOR OBTAINING SPHEROIDAL GRAPHITE CASTINGS [73] Assignee: Pont-A-Mousson S.A.,

Pont-A-Mousson, France [22] Filed: May 8, 1973 [21] Appl. No.: 358,229

[30] Foreign Application Priority Data May 10, 1972 France 72.016809 [52] US. Cl. 164/57; 164/55 [51] Int. Cl. B22D 27/20 [58] Field of Search 164/55, 57

[56] References Cited UNITED STATES PATENTS 2,595,292 5/1952 Reece 75/122 3,658,115 4/1972 Ryntz, Jr. et al. 164/57 3,703,922 11/1972 Dunks et a1 164/57 3,746,078 7/1973 Moore et a1. 164/55 3,819,365 6/1974 McCaulay et al 164/55 FOREIGN PATENTS OR APPLICATIONS 1,132,056 10/1968 United Kingdom 164/55 United Kingdom 164/55 Australia 164/57 OTHER PUBLICATIONS Gating of Ductile iron Castings, by R. W. White, Foundry, Feb. 1960, pp. 101-107.

Primary Examiner-C. W. Lanham Assistant ExaminerV. K. Rising Attorney, Agent, or FirmSughrue, Rothwell, Mion, Zinn & Macpeak ABSTRACT A method for obtaining castings of spheroidal graphite iron, by treatment of the iron with a nodularizing agent, comprising filling a pouring ladle with liquid iron pouring the iron from the ladle into a mould in the form of a stream of iron and incorporating the nodularizing agent into the stream of iron in a region between the pouringladle and the mould and as near as possible to the mould. A device for carrying out said method comprises a pouring ladle and a mould, a pouring channel between the ladle and the mould and a device for supplying nodularizing agent combined with the pouring channel.

4 Claims, 6 Drawing Figures U.S. Patent Nov. 4, 1975 I Sheet1of 2 3,916,979

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F'IG-2 METHOD FOR OBTAINING SPHEROIDAL GRAPHITE CASTINGS The present invention relates to the manufacture of spheroidal graphite castings by treating the iron with a nodularizing agent, such as pure magnesium or magnesium alloy, cerium etc.

According to the known technique, a certain amount of iron is previously treated in a pouring ladle with a nodularizing agent and the treated iron is then poured into the moulds.

Now, it is normally necessary to treat a large amount ofiron at once, ifit is desired to maintain the iron sufficiently hot and if it is desired to have enough iron available for supplying a number of moulds. In practice it even happens that the manufacture, that is to say the casting, has to be stopped until more iron is ready. It also happens that a very large amount of iron, for example of the order of several tons, must be prepared in a pouring ladle in order to cast large parts.

In this case, the known technique of previously treating the iron before pouring it into the moulds has as drawback the fact that the liquid iron treated with a nodularizing agent is adversely affected by awaiting subsequent use and storage. It tends to lose its nodularizing agent so that the proportion of nodules of graphite upon solidification is lower. The graphite can even be completely lamellar.

An object of the invention is to overcome this drawback and to provide a method for obtaining spheroidal graphite castings, by treating the iron with a nodularizing agent, of the type comprising filling a pouring ladle with liquid iron and pouring said iron from said ladle into a mould in the form of a stream, wherein the nodularizing agent is incorporated in the liquid iron in said stream between the pouring ladle and the mould and as near as possible to the mould.

With this method, it is easier to store in the ladle iron which has not been treated with a nodularizing agent and, moreover, surprisingly easier to obtain at any moment castings without loss of nodularizing agent and therefore without reduction of the number of graphite nodules. Indeed, in a surprising manner, the yield of nodularizing agent, that is to say the ratio between the nodularizing agent introduced and the nodularizing agent retained in the iron, and therefore the quality of the castings, are improved. This result is the more surprising in that one would have expected, under such conditions of introduction of the nodularizing agent in the open air, a rapid combustion and vaporization of the nodularizing agent before it is able to react with the iron, which is not the case, as experience has shown.

In one particularly advantageous manner of proceeding, a whirling disturbance or turbulence is created in the flowing stream of liquid iron downstream of the region in which the nodularizing agent is introduced.

Another object of the invention is to provide a device for carrying out said method in the case of\ a static pouring. This device, which is of the type comprising a pouring ladle and a fixed mould, has the feature that it comprises a pouring channel between the ladle and the mould and a device for feeding nodularizing agent combined with said channel.

Further features and advantages of the invention will be apparent from the ensuing description with reference to the accompanying drawings.

In the drawings FIG. 1 is a diagrammatic view of a device according to the invention for carrying out the method according to the invention in the case of pouring iron into a static mould;

FIGS. 2 and 3 represent micrographs showing the comparison of the structures of the spheroidal graphite castings obtained respectively in accordance with the known technique and in accordance with the method according to the invention in respect of a static mould;

FIG. 4 is a diagrammatic view of a device employed in the application of the method according to the invention to the casting of a pipe in a centrifugal casting mould, and

FIGS. 5 and 6 are comparative micrographs, similar to those of FIGS. 2 and 3, in respect of pipes cast by means of the method employing the device described with reference to FIG. 4.

In the embodiment shown in FIG. 1, the basic liquid iron untreated with magnesium contained in a tiltable pouring ladle 1 is poured into a chute 2 extended by a pouring channel 3 which is preferably short (for example 10-50 centimetres long). This pouring channel 3 is inclined and its end is disposed above a pouring cup or funnel 4 of a static mould.

Disposed above the upstream part of the channel 3 is a hopper 6 containing the required powdered nodularizing agent which is selected, for example, from magnesium and the alloys of the iron-silicon-magnesium, iron-silicon-magnesium-rare earths, nickel-magnesium or mischmetal type, the treating powder being very fine (OO.4 mm grain size). This hopper 6 pours the nodularizing agent powder onto the iron by way of an adjustable orifice 7 so that it is possible to adjust the flow of the powder in accordance with the flow of the poured iron. The percentage of nodularizing agent with respect to the weight of the iron is chosen, if this agent contains 5% magnesium, between 0.2 and 2% depending on the nature of the agent, the analysis of the basic iron and the thickness of the part being cast.

In order to promote the incorporation of the nodularizing agent into the iron and its reaction with the latter, the pouring channel 3 is capped, downstream of the point at which the powder of nodularizing agent falls onto the iron, by a detachable hood 8 which is adapted to maintain a number of vertical or inclined bars of graphite 9 in the channel in such manner as to be partly immersed in the flowing stream of iron. These bars 9 are aligned on a longitudinal axis of the channel or may be slightly laterally offset on each side of this axis so as to produce regions of whirling disturbances or turbulence in the stream of iron. Owing to these disturbances, the nodularizing agent powder floating on the surface of the iron is incorporated within the liquid metal immediately before its introduction into the mould 5.

Thus the treatment of the iron by means of the nodularizing agent is carried out practically at the same time as the pouring so that the time which elapses between the addition of the nodularizing agent and the casting proper is negligible so that this nodularizing agent has its maximum effect on the iron. The micrographs shown in FIGS. 2 and 3 illustrate, with a magnification of 100, the structures of the castings on one hand cast in moulds similar to the mould 5 shown in FIG. 1 with an iron previously treated in the pouring ladle according to the known technique (FIG. 2) and, on the other hand, cast by the aforementioned method and device according to the invention (FIG. 3). These two Figures represent the structure of two castings having a thickness of 4mm. In comparing these castings, it is seen that the number of graphite nodules per unit area is much higher in FIG. 3 (2,500 nodules/sq.mm) than in FIG. 2 (700 nodules/sq.mm). Moreover, it will be observed that the obtained increase in the number of nodules results in a more ferritic structure (FIG. 3) and therefore in improved as-cast characteristics. in particular the elongation and resilience.

The following two examples comparing the known method and the method according to the invention also reveal the improved yield in nodularizing agent:

EXAMPLE No. 1

Prior Art A basic iron having as mean analysis C 3.8%, Si 1.9%..S 0.007%, the remainder being iron, was treated ina ladle by the known method with 1.4%, with respect to the weight of the iron, of a nodularizing alloy Fe-Si-Mg containing 9% Mg. The yield of Mg was The iron thus treated gave, after inoculation with 0.3% by weight of a graphitizing alloy Fe-Si having 75% Si. a spheroidal graphite iron having 700 nodules/sq.mm and 60% pearlite (FIG. 2).

EXAMPLE No. 2

Method According to the Invention With the same basic iron as in the preceding example, there was introduced by the method according to the'invention 2%, with respect to the weight of the iron, ofa mixture comprising 50 parts by weight ofa nodularizing alloy Fe-Si-Mg having 12% Mg and 50 parts by weight of a graphitizing alloy having 75% Si. Thus 1% nodularizing agent, with respect to the weight of the iron, was employed. The yield of Mg was 35%. The iron thus treated gave a spheroidal graphite iron having 2,500 nodules/sq.mm and a few traces of pearlite (FIG.

The method according to the invention is particularly advantageous when large pouring ladles are employed containing several tons of iron, for example 10 metric tons of iron, for filling a large number of moulds or for i casting large foundry parts, since there is no prior combustion and vaporization of the nodularizing agent (for example magnesium) in the large pouring ladle because the latter only contains ordinary as yet untreated iron in the method according to the invention.

In the modification shown in FIG. 4, the invention is applied to the casting of a pipe by means ofa device of the type described in French Pat. No. 1,456,844. This device comprisesa centrifugal casting mould 11 and a tiltable ladle 12 from which the iron is poured into a chute 13 extended by a pouring channel 14 which extends into the mould 11. The channel and the mould undergo a relative movement of translation parallel to the channel and to the axis of the mould, the mould being itself rotated about its axis. This pouring channel therefore differs from the pouring channel 3 of the preceding embodiment by its great length.

Above the upstream part of the channel 14, there is disposed a hopper 15 containing the amount of nodularizing agent powder required for treating the iron. This hopper pours the powder onto the iron by way of an adjustable orifice l6 which permits adjusting the flow of the powder in accordance with the flow of iron, for example by means of a needle valve member 17 actuated by a screw 18 having a control handle 19. The channel 14 is covered downstream of the region in which the powder falls onto the iron by a detachable hood 20 which is adapted to maintain a number of bars 21 of graphite which extend inwardly of the channel to an extent which is sufficient to immerse the bars in the stream of molten iron.

The micrographic structures shown in FIGS. 5 and 6 permit a comparison of the results obtained by the prior art and those obtained by the method according to the invention. They represent structures of the iron halfway through the thickness of the wall of pipes having a nominal diameter of 800 mm and a wall thickness of 12 mm. The following comparative examples show the surprising improvement in the results obtained by the method according to the invention in which the nodularizing agent is added to the stream of iron just before the introduction of the iron in the centrifugal casting mould, the agent being mixed with the iron by the creation of whirling disturbances or turbulence by the graphite bars 21.

EXAMPLE No. 3

Prior Art There was previously treated in a pouring ladle a basic iron having as analysis C 3.60%, Si 2.20%, S 0.005% with 0.1% by weight of nodularizing Mg. The iron thus treated in the ladle was cast in the centrifugal casting mould in the form ofa pipe having a weight of 1,600 kg a nominal diameter of 800 mm, a length of 7 m and a wall thickness of 12 mm. The yield of Mg was 20%. After inoculation, in the chute l3 upstream of the pouring channel 14, with 0.8% graphitizing Fe-Si having Si, there was obtained, as shown in FIG. 5, an iron containing 800 nodules/sq.mm and 50% pearlite halfway through the thickness of the wall of the pipe (magnification EXAMPLE No. 4

Method According to the Invention The same basic iron was employed and treated in the pouring channel 14 with 0.9% by weight of nodularizing alloy Fe-Si-Mg containing 5% Mg and 1% rare earths by weight. It was found that, as shown in FIG. 6, the graphite 22 of the pipe is completely spheroidal and the yield of Mg was 35%. After inoculation at the downstream end of the channel 14 with 0.9% graphitizing Fe-Si containing 80% Si, an iron was obtained containing 1,600 nodules/sq.mm and 30% pearlite halfway through the thickness of the wall of the pipe (magnification 100).

Examples similar to the preceding examples and carried out with proportions varying from 0.8 to 1% by weight of nodularizing agent containing 1% Mg and 1% rare earths, namely with 0.04 to 0.05% Mg, showed that such a proportion is sufficient to obtain castings whose graphite is completely spheroidal whereas by the known method of previously treating the iron in the ladle, a much higher proportion of magnesium was necessary, namely of the order of 0.09 to 0.19% of pure magnesium, the graphite tending to become compact instead of spheroidal below these percentages, in particular on the inner surface of pipes cast by centrifugal casting methods.

Within the limits of the indicated values, the proportion of nodularizing agent employed depends, on one hand, on the rate of solidification of the casting, which is a function of the thickness of the casting (the thicker the casting the higher the content of Mg necessary to render the iron spheroidal graphite iron) and, on the other hand, on the content of sulphur and oligo elements in the basic iron.

Other examples similar to the foregoing examples, but carried out for different castings, showed that the invention is applicable not only to the casting of foundry parts of any type, and advantageously large foundry parts, but also to the manufacture of centrifugally cast pipes of small, medium and large diameters, and advantageously in respect of the latter, having a diameter of 700 to 2,000 mm, a length of 6-9 m and a wall thickness exceeding 10 mm, the iron being treated in the channel 14 with a proportion of 0.52% of an alloy of Fe-Si-Mg-rare earths containing 5% Mg and 1% rare earths. In respect of castings having a wall thickness of less than 10 mm, 02-07% of nodularizing alloy containing 5% Mg may be employed.

We claim:

1. A method for obtaining castings of spheroidal graphite iron, by treatment of the iron with a powdered nodularizing agent, comprising filling a pouring ladle with liquid iron and pouring the iron from the ladle into an upstream end of a pouring trough which has a downstream end for pouring the liquid iron into a mould so that the iron flows in the trough in the form of a stream of iron, and incorporating the powdered nodularizing agent into the stream of iron in a region between the upstream end and downstream end of the trough and as near as possible to the downstream end of the trough, the flow of powdered nodularizing agent supplied to the liquid iron being adjusted in accordance with the flow of iron, and creating a turbulence in the stream of iron downstream of the region in which the nodularizing agent is incorporated.

2. A method as claimed in claim 1, wherein said tur bulence is created in at least the upper surface of the stream of iron.

3. A method as claimed in claim 1, comprising, in the case where the nodularizing agent is a Fe-Si-Mg alloy containing 12% magnesium, adding said agent to the iron in a proportion of about 1% by weight with respect to the iron poured.

4. A method as claimed in claim 1, comprising, in the case where the nodularizing agent is a Fe-Si-Mg-rare earths alloy containing 5% magnesium and 1% rare earths, adding said agent to the iron in a proportion of substantially 0.2-2% by weight with respect to the iron poured. 

1. A METHOD FOR OBTAINING CASTINGS OF SPHEROIDAL GRAPHITE IRON, BY TREATMENT OF THE IRON WITH A POWDERED NODULARIZING AGENT, COMPRISING FILLING A POURING LADLE WITH LIQUID IRON AND POURING THE IRON FROM THE LADLE INTO AN UPSTREAM END OF A POURING TROUGH WHICH HAS A DOWNSTREAM END FOR POURING THE LIQUID IRON INTO A MOULD SO THAT TH IRON FLOWS IN THE TROUGH IN THE FORM OF A STREAM OF IRON, AND INCORPORATING THE POWDERED NODULARIZING AGENT INTO THE STREAM OF IRON IN A REGION BETWEEN THE UPSTREAM END AND DOWNSTREAM END OF THE TROUGH AND AS NEAR AS POSSIBLE TO THE DOWNSTREAM END OF THE TROUGH, THE FLOW OF POWDERED NODULARIZING AGENT SUPPLIED TO THE LIQUID IRON BEING ADJUSTED IN ACCORDANCE WITH THE FLOW OF IRON, AND CREATING A TURBULENCE IN THE STREAM OF IRON DOWNSTREAM OF THE REGION IN WHICH THE NODULARIZING AGENTS INCORPORATED.
 2. A method as claimed in claim 1, wherein said turbulence is created in at least the upper surface of the stream of iron.
 3. A method as claimed in claim 1, comprising, in the case where the nodularizing agent is a Fe-Si-Mg alloy containing 12% magnesium, adding said agent to the iron in a proportion of about 1% by weight with respect to the iron poured.
 4. A method as claimed in claim 1, comprising, in the case where the nodularizing agent is a Fe-Si-Mg-rare earths alloy containing 5% magnesium and 1% rare earths, adding said agent to the iron in a proportion of substantially 0.2-2% by weight with respect to the iron poured. 